• in 6-month-old mice, a 2-fold decrease in bone formation rate (BFR) is observed; similar results are seen in 2- and 4-month-old animals

• this is due to decreased matrix apposition rate (MAR - amount of bone matrix deposited per osteoblast cluster; 0.75 um/day vs 0.45 um/day in wild-type); similar results are seen in 2- and 4-month-old animals